First of all, everybody uses the "intuitive UI" expression, but actually, quite a lot of designer can define objectively what it is. Everett McKay knows, he defines perfectly: "If your target users must resort to reason, memorizing, experimenting, seeking help, or training, your UI isn’t intuitive by definition.” As a UX designer, I learned a lot from this book, for example how to use this approach in heuristic evaluations. Quite useful for all level of UX practitioners and for web designers as well.